Schizophrenia: the dopamine hypothesis

The original hypothesis

The dopamine hypothesis says schizophrenia, especially its positive symptoms, is linked to too much dopamine activity, particularly overactivity at D2 receptors in the brain.

Dopamine is a neurotransmitter released at synapses. Excess activity could come from releasing too much dopamine, having too many D2 receptors, or receptors being over-sensitive.

The revised hypothesis

Later versions suggest different pathways matter:

• Mesolimbic pathway (to the limbic system): hyperactive dopamine causing D2 over-stimulation and positive symptoms (hallucinations, delusions).
• Mesocortical pathway (to the prefrontal cortex): hypoactive dopamine (less D1 stimulation), linked to negative symptoms and cognitive problems.

So schizophrenia may involve both too much and too little dopamine in different areas.

Evidence for

• Drugs that raise dopamine (amphetamine, cocaine) can produce psychosis-like symptoms and worsen symptoms in patients.
• Antipsychotics block D2 receptors and reduce positive symptoms; Creese, Burt and Snyder (1976) and Seeman et al. (1976) found that drugs that bind D2 more strongly are clinically more potent.
• Imaging: some studies show greater striatal dopamine release after amphetamine in patients, and Wong et al. (1986) reported more D2 receptors in drug-naive patients.

Evidence against and evaluation

• Time lag: antipsychotics block dopamine within hours, but symptoms take days or weeks to improve, so dopamine may be only indirectly involved.
• Not everyone responds: some patients (treatment-resistant schizophrenia) still have symptoms even when antipsychotics block most of their D2 receptors.
• Inconsistent imaging: several studies of drug-naive patients found no D2 difference.
• Glutamate: drugs such as PCP and ketamine block NMDA glutamate receptors and cause positive and negative symptoms, so other neurotransmitters are involved.
• Reductionism (9.3.3): it reduces a complex illness to one chemical and ignores stress and family factors; it cannot say whether dopamine changes are a cause or an effect.
• Application: it led to effective drug treatments that let many people live outside hospital.

Worked example

Evaluate the claim that amphetamine research supports the dopamine hypothesis.

1. Amphetamine increases dopamine and can produce hallucinations and paranoia in healthy users and worsen symptoms in patients, so raised dopamine is linked to positive symptoms.
2. This supports the idea that dopamine excess can cause psychotic symptoms.
3. However, amphetamine-induced psychosis is not identical to schizophrenia (for example, fewer negative symptoms), and amphetamine affects other chemicals too.
4. Judgement: it supports a role for dopamine in positive symptoms but not dopamine as the whole cause.

Answer: Supportive for positive symptoms, but it does not show dopamine is the sole cause.

Check yourself

1. Which receptor is most associated with the original dopamine hypothesis?
   • D1
   • NMDA
   • D2
   • 5-HT1A
   Show answer

   D2. Antipsychotics block D2 receptors.

2. According to the revised hypothesis, overactivity in which pathway is linked to positive symptoms?
   • Mesolimbic
   • Mesocortical
   • Nigrostriatal only
   • Spinal
   Show answer

   Mesolimbic. Mesolimbic hyperactivity is linked to positive symptoms.

3. Why does the time lag in antipsychotic effects challenge the dopamine hypothesis?
   • Antipsychotics increase dopamine
   • Patients stop taking the drugs immediately
   • Dopamine is blocked within hours but symptoms improve over days or weeks
   • Dopamine cannot be measured
   Show answer

   Dopamine is blocked within hours but symptoms improve over days or weeks. If dopamine were the direct cause, symptoms should improve as soon as it is blocked.

4. Which finding suggests neurotransmitters other than dopamine are involved?
   • Amphetamine worsens psychotic symptoms
   • PCP and ketamine, which block NMDA receptors, produce schizophrenia-like symptoms
   • Antipsychotics block D2 receptors
   • D2 binding predicts drug potency
   Show answer

   PCP and ketamine, which block NMDA receptors, produce schizophrenia-like symptoms. NMDA receptors are glutamate receptors, so glutamate is implicated.

5. Explain how antipsychotic drugs provide evidence for the dopamine hypothesis.
   Show answer

   Antipsychotics block dopamine D2 receptors and reduce positive symptoms such as hallucinations, which suggests that too much dopamine activity causes those symptoms.. Blocking dopamine reduces symptoms, implying dopamine excess.

6. Explain why the dopamine hypothesis can be criticised as reductionist.
   Show answer

   It explains a complex disorder only in terms of one neurotransmitter, ignoring other factors such as stress, family environment and other neurotransmitters like glutamate.. Reductionism: one chemical explains a complex disorder.

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Sources

• Pearson Edexcel International Advanced Subsidiary/Advanced Level in Psychology specification (issue January 2026)
• Pearson IAL Psychology component guide: WPS04 (Issue 2, November 2024)
• Howes and Kapur (2009), The dopamine hypothesis of schizophrenia: version III, the final common pathway, Schizophrenia Bulletin
• Psychiatric Times: Glutamate and schizophrenia, theory and treatment implications
• Pearson WPS04/01 examiners' report, June 2025

Last updated 8 November 2026. Spotted a mistake? Tell us.